Transcranial magnetic stimulation of the dorsolateral prefrontal cortex was used to measure thresholds of individual perception and motor response in three groups of subjects: 1) subjectively electrosensitive people, 2) general population controls with a high burden of complaints related to electromagnetic field exposure, and 3) general population controls with a low burden of complaints.
Perception thresholds under double blind conditions as well as objectively measured motor thresholds for evoked potentials were determined by applying singular transcranial magnetic pulses to the motor cortex.
|Setup||Perception thresholds were determined by stimulating subjects with a figure-8 coil (double circular 70-mm coil) placed over the left dorsolateral prefrontal cortex (DLPFC), as usually done in rTMS studies treating depressive patients [Eichhammer et al., 2002], but using singular stimuli.|
|Sham exposure||A sham exposure was conducted.|
|Additional info||A specific sham coil was used imitating the characteristic acoustic click associated with an active stimulation but not inducing a magnetic field. Active and sham coils were handed out according to a randomization scheme for the four series (ABAB versus BABA) so that both the subjects and the physicians applying the coils remained blinded.|
|Chamber||Resting (RMT) and active (AMT) motor thresholds, representing paradigms of cortical excitability, were measured by TMS according to [Rossini et al., 1994].|
|Setup||The coil was held with the junction of the two wings tangential to the skull and the handle pointing backwards and 45° away from the midline. Thus, the induced current in the brain was directed about perpendicular to the assumed line of the central sulcus.|
|Additional info||Motor evoked potentials (MEP) from the right abductor digiti minimi muscle were recorded using surface electrodes in a belly-tendon montage. MEP amplitudes were measured peak to peak in 10 consecutive trials for each stimulus intensity.|
No parameters are specified for this exposure.
There were no significant differences between groups in the thresholds, neither of detecting the real magnetic stimulus nor in motor response. But the three groups differed significantly in differentiating between stimulation and sham condition. The subjectively electrosensitive people have the lowest ability to differentiate and the control group with high level of electromagnetic field-related complaints has the best ability to differentiate. Differences between groups were mostly due to false alarm reactions in the sham condition reported by subjectively electrosensitives.
The authors found no objective correlation of the self perception of being "electrosensitive." Overall, the experiment does not support the hypothesis that subjectively electrosensitive patients suffer from a physiological hypersensitivity to electromagnetic fields or stimuli.